Korean students drop -ed past tense mid-sentence: why it happens and how to drill it out

You've heard it a thousand times by October. A student with decent vocabulary, clear pronunciation, maybe even solid grammar on a worksheet, stands up and says "Yesterday I go to the park." You correct it. Two minutes later: "Last week my mom buy new shoes."

It is not carelessness. The reason sits in the structure of Korean itself.

Why Korean speakers drop -ed

Korean verbs do change to show tense, but not the way English does. In English, the verb carries the tense marker every single time: walk becomes walked, buy becomes bought. Miss the ending and the sentence breaks.

In Korean, tense is often marked once at the end of the clause, and sometimes it is carried by a time word rather than the verb ending at all. A sentence like "어제 학교에 갔어요" literally sequences as "yesterday / school / went," but the verb ending -았- is doing less work than the word 어제. The time word does half the job. You can drop tense marking in casual speech and still be understood, because context and time words fill the gap.

So when a Korean seven-year-old learns English, their brain expects time words to do more work than they actually do in English. "Yesterday" feels like it should be enough. Adding -ed feels redundant.

The error fossilises fast, because in early elementary the teacher usually understands them anyway.

What doesn't work

Explaining the rule again does nothing. They know the rule. Most of them can conjugate walk → walked on a worksheet perfectly. The problem is not knowledge, it is production under pressure.

Gap-fill exercises help a little, but only if the student has five seconds to think. In real speech they don't.

What does work: forced contrast drills

You need drills that make the student produce both forms in quick succession, so the brain starts to feel the difference as physical, not theoretical.

Drill 1: Yesterday/Today chain (whole class, 8 minutes)

Stand at the front. Say a verb in present tense and point at a student.

Teacher: "I eat pizza." Student 1: "Yesterday I ate pizza." Teacher: "Good. Today I walk to school." Student 2: "Yesterday I walked to school."

No time to think. If they drop the -ed, snap your fingers and they redo it immediately. Move fast. Thirty verbs in eight minutes.

Drill 2: Timeline draw (pairs, 10 minutes)

Give each pair a blank timeline: a horizontal line with "yesterday" on the left, "today" in the middle, "tomorrow" on the right.

Read out ten sentences in mixed tenses. Students draw a dot on the timeline where the action happened, then write the sentence under the correct section. Check by having them read their "yesterday" sentences aloud in a chain. Every single one should have -ed or an irregular past form.

Drill 3: True sentence swap (pairs, 6 minutes)

Student A says something true about yesterday. Student B repeats it in the third person, then says their own sentence.

A: "Yesterday I played computer games." B: "Yesterday she played computer games. Yesterday I watched TV." A: "Yesterday he watched TV. Yesterday I..."

If either student drops -ed, their partner catches it and they redo the sentence before continuing. Do not let errors slide, even once.

When to drill

This is not a one-week unit. You need to loop it back every ten days for the first three months, then monthly until June. Five minutes at the start of class, always with a different drill format so it doesn't feel like the same punishment.

The first time you run any of these drills, half the class will stumble. By the fourth or fifth cycle, the error rate drops visibly. By December, most students self-correct mid-word without prompting.

One thing we don't know

We have never found a clean way to explain why irregular past forms (go → went, buy → bought) are easier for Korean students to remember than regular -ed endings. They just are. If you work out why, write it down.