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One marshmallow now or two later? Should have and could have for regrets and missed chances

This B2 ESL lesson plan teaches should have, shouldn't have and could have through the marshmallow test, the Stanford preschool studies of one treat now or two later.

Grammar
Should have and shouldn't have + past participle for regrets and criticism, could have for missed chances (I could have had two.), questions, and should for advice.
Topic
What Walter Mischel's team found about waiting and why later studies disagree, with words such as resist, temptation and replicate.
Activities
An explainer to read, an office argument and a teacher's memo to hear, self-checking drills, a chat about an impulse buy and boxes about regrets.

What's inside

  1. Chapter 1Warm-up: now or later?

    • PictureUnlock
    • Spin the wheel and answerSpin the wheelUnlock
    • Study the words: waiting and wantingVocabularyTry it
    • Look at the pictures and choose the wordChoose by pictureUnlock

  2. Chapter 2One treat now, two treats later

    • Look at the photo: a preschool game roomPictureUnlock
    • Read Leona's explainer on The Why DeskArticleUnlock
    • Read and mark true or falseTrue or falseUnlock
    • Read again and choose the correct answerQuizUnlock
    • Match the paragraphs and the headingsMatchUnlock

  3. Chapter 3Who ate the meeting donuts?

    • Listen to Leona and IsaiahListeningTry it
    • Transcript, for the teacherUnlock
    • Listen and choose the correct answerQuizUnlock
    • Listen to the Reader's Rebuttal: Tom's voice memoListeningUnlock
    • Transcript, for the teacherUnlock
    • Listen and mark true or falseTrue or falseUnlock

  4. Chapter 4Grammar: I could have had two

    • Study the scheme: I should have waitedGrammar schemeTry it
    • Choose the correct optionChoose the optionUnlock
    • Fill in the gaps: use the words in bracketsFill in the gapsTry it
    • Fill in the table: should or should have?Fill in the tableUnlock
    • Choose the correct answer: what does it mean?QuizUnlock
    • Put the words in the correct orderUnjumbleUnlock

  5. Chapter 5Let's talk: I should have slept on it

    • Choose the right replies: a friend's impulse buyChatTry it
    • Open a box and answer: now or later?Open the boxUnlock

  6. Chapter 6Homework

    • Match the words and the meaningsMatchUnlock
    • Unscramble the wordsAnagramUnlock
    • Fill in the gaps with the lesson's wordsFill in the gapsUnlock
    • Find the matching pairs: words and meaningsMemory gameUnlock
    • Choose the correct option: new sentencesChoose the optionUnlock
    • Fill in the gaps: use the words in bracketsFill in the gapsUnlock
    • Choose the correct answer: which sentence is correct?QuizUnlock
    • Put the words in the correct order: new sentencesUnjumbleUnlock
    • Choose the correct option: an advice columnChoose the optionUnlock
    • Drag the words into the gaps: Leona answers TomDrag and dropUnlock

33 exercises in 6 chapters. Start a 7-day free trial to open all of them, copy any part into your own lessons, and teach the lesson live.

Vocabulary

12 words and phrases from the lesson, each with a picture and audio in edio.

+9 more with pictures and audio in the lessonMore words

  • regret
  • impulse
  • temptation
  • self-control
  • one-way window
  • chewy
  • reliable
  • pay off
  • replicate

Grammar: should have, shouldn't have and could have

These forms judge a past that can't change: should have + past participle for the right thing that didn't happen, shouldn't have for a mistake that did, and could have for a chance nobody took. A child who rang the bell early could have had two treats, so the test suits all three.

I should have waited. I could have had two.

Look back at the past with should have, shouldn't have and could have + the past participle: regrets, criticism and chances you missed.

Three forms, three meanings

I should have waited means I didn't, and I'm sorry. You shouldn't have opened the box means you did, and it was a mistake. I could have had two means two were possible, but I had one. The form never changes with the person.

Three forms, three meanings

FormWhat it meansExample
should have + past participleIt was the right thing to do, but it didn't happen: a regret or a criticism.I should have waited. (I didn't wait.)
shouldn't have + past participleIt happened, but it was a mistake.You shouldn't have opened the box. (You opened it.)
could have + past participleIt was possible, but it didn't happen: a missed chance.I could have had two marshmallows. (I had one.)

Every person: the form never changes

Personshould haveshouldn't havecould have
II should have waited.I shouldn't have eaten it.I could have had two.
youYou should have waited.You shouldn't have eaten it.You could have had two.
heHe should have waited.He shouldn't have eaten it.He could have had two.
sheShe should have waited.She shouldn't have eaten it.She could have had two.
itIt should have worked.It shouldn't have broken.It could have been worse.
weWe should have waited.We shouldn't have eaten it.We could have had two.
theyThey should have waited.They shouldn't have eaten it.They could have had two.

Questions and short answers

Should or could comes first, then the subject, then have + participle: Should I have waited? What should she have done? Short answers stop at have: Yes, you should have. No, you shouldn't have.

QuestionAnswer
Should I have waited?Yes, you should have. / No, you shouldn't have.
What should she have done?She should have hidden the box.
Could they have waited longer?Yes, they could have, with a better trick.

Advice for next time, or a look back?

Should + base form gives advice for now or later: Next time, you should hide the box. Should have + participle judges what already happened: Yesterday, you should have hidden the box. A time word often decides.

should + base form: advice for now or later

  • You should wait.
  • Next time, you should hide the box.
  • You shouldn't eat it now.

should have + past participle: a look back

  • You should have waited.
  • Yesterday, you should have hidden the box.
  • You shouldn't have eaten it.

Have, not of, then the past participle

In fast speech, should've sounds almost like should of, but always write have or 've. After have comes the past participle, not the base form or the past simple: should have waited, should have taken, not should have wait or should have took.

Write have, then the past participle

In fast speech, should have and could have sound like “should've” and “could've”, almost like “should of”. But always write have (or 've), never of. After have, use the past participle: should have waited, eaten, hidden, rung, taken (not: should have wait, could had, should have took).

Could have as criticism, and shouldn't have to

Could have can complain too: You could have asked me! means you didn't, and you should have. Keep shouldn't have eaten apart from shouldn't have to wait: the first is a past mistake, the second means “it isn't necessary or fair.”

Two look-alikes

could have can criticize too: You could have asked me! (= You didn't ask, and you should have.) And don't mix up shouldn't have + past participle, a past mistake (You shouldn't have waited.), with shouldn't have to + base form, which means “it isn't necessary or fair” (You shouldn't have to wait so long.).

At The Why Desk

  • Isaiah should have waited for the meeting.
  • He shouldn't have opened the box.
  • Leona could have hidden the donuts.
  • “How could I have known?” Isaiah asked.
  • Some researchers say the 2018 team shouldn't have counted so many factors.
  • A child who rang the bell could have had two treats.

Common mistakes

Four slips: I should of waited, You should have wait, I could had two and I shouldn't have to eat them last night. The fixes are should have waited, could have had and, for a past mistake, shouldn't have eaten.

  • I should of waited.

    I should have waited.

    write have (or 've), never of

  • You should have wait.

    You should have waited.

    have + the past participle

  • I could had two.

    I could have had two.

    could + have + past participle

  • I shouldn't have to eat them last night.

    I shouldn't have eaten them last night.

    a past mistake: shouldn't have + past participle

More lessons on this grammar: Modal verbs lessons and exercises

Try the should have and could have exercises

Try them yourself: these are the same exercises your students do in edio.

More exercises

What's in the lesson

  • 18 auto-checked exercises
  • 6 games
  • 1 article
  • 1 grammar scheme
  • 1 set of word cards
  • 2 audio clips
  • 2 pictures
  • 2 transcripts

The main objectives of this lesson are to:

  • regret or criticize a past action: I should have waited. You shouldn't have opened the box.
  • name a missed chance or complain about one with could have: I could have had two marshmallows. You could have asked me!
  • ask and answer about the past: Should I have waited? – Yes, you should have. What should she have done?
  • tell advice for next time from a look back: Next time, you should hide the box against Yesterday, you should have hidden it.
  • write should have, never should of, with the right participle: could have taken, not could had or could have took

Lesson 22 is the second lesson of Money and smart choices, unit 6 of English B2.1 · How the World Works. Its modal + have + past participle is the shape of would have in the third conditional of lesson 5, and it looks back at the past like wish + past perfect in lesson 19. Lesson 23 turns to prepositions for numbers. A child who ate one treat and missed the second is the plainest case of I could have had two.

Students spin a wheel of questions about waiting and wanting, then learn twelve words, from resist and grab to one-way window and replicate, with pictures and audio. They read Leona's explainer on the Stanford studies and their critics, then hear Leona and Isaiah argue over the meeting donuts he ate and Tom, a kindergarten teacher from California, argue that trust matters more; both are AI-voiced. The grammar chapter has the scheme and five self-checking drills, among them a table that sets should against should have. Then students talk a friend through an impulse buy and open boxes about now or later.

All ten homework tasks check themselves: a word match, an anagram, a gap-fill and a memory game on the words; then new sentences with forms to choose, gaps with irregular participles, a quiz on correct sentences, sentences to put in order, an advice column on a spent paycheck, and Leona's answer to Tom with words to drag in.

Grammar:
should have · shouldn't have · could have · past modals for regrets and criticism · should vs should have
Topic:
the marshmallow test · Walter Mischel · Stanford's Bing Nursery School · self-control · trust and waiting · money and smart choices · The Why Desk

Teaching tips

  • Draw two plates on the board, one with a marshmallow and one with two, before the reading. Ask what a four-year-old would do and what might help a child wait, then compare with the tricks in Leona's explainer.
  • Sort each form by one question: did it happen? Should have: no, but it was right. Shouldn't have: yes, and it was wrong. Could have: no, but it was possible.
  • Play the donut argument twice: first to decide who blames whom, then to catch every past modal: You should have waited. You could have hidden them. How could I have known?
  • Collect a class list of small regrets before the chat: a late night, an impulse buy, a missed bus. Each student says what they should have done and what they could have done instead.

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The whole course: English B2.1 · How the World Works

32 lessons for adults at B2 in American English, each answering one question about how the world works. The team of The Why Desk, a small online magazine in Pittsburgh, takes on one question a week, from the day a computer beat the world chess champion to eight people sealed inside Biosphere 2. Learners tell stories with narrative tenses, speculate about the past and the future, and report what experts claim. The practice exercises check themselves.See the course

  1. Unit 1 AI and the future of work

    narrative tenses, by and until, be bound to and be likely to, the future perfect

    1. Lesson 1Checkmate: the day a computer beat the championNarrative tenses: past simple, past continuous and past perfect
    2. Lesson 2The robot car that crossed the desertTime prepositions: by, until, within, throughout, in time and on time
    3. Lesson 3Can a chatbot fool you?Probability about the future: be bound to, be likely to, the chances are
    4. Lesson 4By 2035, what will AI have designed?The future perfect simple: will have + past participle

  2. Unit 2 Health breakthroughs

    the third conditional, the past perfect and past continuous passive, have something done, the passive with two objects

    1. Lesson 5The moldy melon that changed medicineThe third conditional: if + had done, would have done
    2. Lesson 61.8 million Polio PioneersThe past perfect passive and the past continuous passive
    3. Lesson 7One clinic, many doctorsHave / get something done
    4. Lesson 8A kidney from a twinThe passive with two objects

  3. Unit 3 Moving people

    the past perfect continuous, the passive infinitive and -ing form, it's worth and there's no point, the future in the past

    1. Lesson 9Six years to the golden spikeThe past perfect continuous vs the past perfect simple
    2. Lesson 10Riding a pod with no driverThe passive infinitive and the passive -ing form
    3. Lesson 11The town that painted bike lanes firstIt's worth, there's no point and it's no use + -ing
    4. Lesson 12The highways that were supposed to take 13 yearsThe future in the past

  4. Unit 4 Wildlife comebacks

    reporting verbs with a that clause, with an object and infinitive and with -ing, verbs of perception

    1. Lesson 13Did wolves really change Yellowstone's rivers?Reporting verbs + that clause
    2. Lesson 14Bringing a parrot back from the edgeReporting verbs + object + (not) to + base form
    3. Lesson 15The beavers that came by parachuteReporting verbs + -ing and verb + preposition + -ing
    4. Lesson 16Fifteen bison take the trainVerbs of perception + object + base form or -ing

  5. Unit 5 Pop culture goes global

    comment adverbs, wish and if only for the present and the past, have someone do and get someone to do

    1. Lesson 17The party that started hip hopComment adverbs: apparently, supposedly, undoubtedly
    2. Lesson 18Slide to the left!Wish and if only for wishes about now
    3. Lesson 19If only they'd kept SupermanWish and if only + past perfect for regrets
    4. Lesson 20The hit factory on West Grand BoulevardCausative have and get: have someone do, get someone to do

  6. Unit 6 Money and smart choices

    -ever words and no matter, should have and could have, prepositions for numbers and change, it's time and would rather

    1. Lesson 21The bank that never closed-ever words and no matter
    2. Lesson 22 · you're hereOne marshmallow now or two later?Should have, shouldn't have and could have
    3. Lesson 23Benjamin Franklin's 200-year giftPrepositions for numbers and change
    4. Lesson 24Why buy a drill you'll use once?It's (high) time and would rather + past simple

  7. Unit 7 Language and communication

    must have, might have and can't have, verb prefixes and suffixes, past modals in continuous and passive forms, agreement with quantities

    1. Lesson 25How did one man write down a language?Past modals of deduction: must have, might have, can't have
    2. Lesson 26Why do Americans write “color”?Verb prefixes and suffixes: misspell, rewrite, simplify, shorten
    3. Lesson 27The joke that needed a smileyPast modals in continuous and passive forms
    4. Lesson 28Can preschoolers save a language?Subject-verb agreement with quantities and collective nouns

  8. Unit 8 Exploring the extremes

    dimension nouns, the future continuous and future perfect continuous, compound adjectives, only, even and just

    1. Lesson 29A walk on the ocean floorDimension nouns and phrases: depth, width, height
    2. Lesson 30Six months of night at the South PoleThe future continuous and the future perfect continuous
    3. Lesson 31Flying on pedal powerCompound adjectives with numbers and participles
    4. Lesson 32Two years under glassFocus adverbs: only, even, just and at all

Questions about this lesson

What does “should have” mean?
Should have + past participle looks back at something that was right but didn't happen, so it carries a regret or a criticism: I should have waited (I didn't wait). The negative, shouldn't have, says something happened and was a mistake: You shouldn't have opened the box. The B2 lesson One marshmallow now or two later? on edio.ai teaches it with the marshmallow test.
How do you form should have and could have?
Use should or could + have + the past participle, the same for every person: I should have waited, she could have had two, they shouldn't have eaten it. Questions put the modal first (Should I have waited?), and short answers end at have: Yes, you should have. In speech, should've and could've are common. The scheme in One marshmallow now or two later? on edio.ai has a table for all seven persons.
What's the difference between should have, could have and would have?
Should have says what was right, could have says what was possible, and would have gives an imagined result, often after an if clause: If I had waited, I would have had two. All three look back at a past that is over. One marshmallow now or two later? on edio.ai teaches the first two; would have belongs to the third conditional of lesson 5 in the same B2.1 course.
What's the difference between should and should have?
Should + base form gives advice for now or the future: Next time, you should hide the box. Should have + past participle judges something that is already over: Yesterday, you should have hidden the box. A time word usually tells you which one you need. A table in One marshmallow now or two later? on edio.ai asks for both forms of eight verbs, one for next time and one for yesterday.
Is it “should of” or “should have”?
Write should have or should've, never should of. In fast speech should've sounds like should of, which is where the mistake comes from. After have, use the past participle: should have waited, could have taken, not should have wait or could had. The chat in One marshmallow now or two later? on edio.ai offers slips like these as wrong replies.
What was the marshmallow experiment?
In the late 1960s and early 1970s, psychologist Walter Mischel and his students tested preschoolers at the Bing Nursery School on the Stanford campus. A child could have one treat now, or two later by waiting for the researcher to come back; ringing a bell ended the wait. The treats varied, from a marshmallow to a pretzel, and Mischel's first question was what helps children wait. One marshmallow now or two later? on edio.ai explains it.
Did later studies confirm the marshmallow test?
Experts still argue about it. In 2018, Watts, Duncan and Quan used a larger, more varied group of American children: the link between waiting and achievement at 15 was about half as strong as in the first studies, and much weaker once family background was counted. Other researchers question that reading, and a 2024 study found the test doesn't reliably predict adult life at 26. One marshmallow now or two later? on edio.ai lays out both sides.
How do I teach should have and could have to B2 students?
Start from one small, clear mistake, such as eating a treat that was meant for later, and ask what the person should have done and could have done. Then set should for next time against should have for yesterday. One marshmallow now or two later? on edio.ai goes from Leona's explainer and the donut argument to the scheme, a gap-fill with words in brackets and four more drills.
What's a good game for practicing should have?
Play “Bad day”: one student reads out a run of bad luck (I overslept, missed the bus and forgot my lunch), and the class answers in turns: You should have set an alarm. You could have taken a taxi. For speaking, the boxes in One marshmallow now or two later? on edio.ai ask Think of a choice you regret. What should you have done instead?
What's good homework for should have and could have?
Good homework gives a believable mistake to judge: an advice column where a teen spent a first paycheck in one weekend works well, with gaps for should have saved, could have put and should make for next time. All ten homework tasks in One marshmallow now or two later? on edio.ai check themselves, with irregular participles and Leona's answer to a reader.
How do you practice should have one-to-one?
Swap stories of small regrets: the student tells a recent mistake, the teacher answers You should have… or You could have…, then they switch roles and the teacher asks What should I have done? The chat in One marshmallow now or two later? on edio.ai needs no partner: a friend spent his class trip savings on a drone at midnight, and the student replies.
Are there interactive exercises for should have and could have?
Yes. This page plays three parts of One marshmallow now or two later?, a B2 lesson on edio.ai, without an account: Leona and Isaiah's argument about the meeting donuts, a gap-fill that builds each form from brackets and a chat about a friend's impulse buy. The other chapters open with an account.
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