小学英语中“写作业”的表达是 do homework。例如：

1. It's time to do my homework.

2. I need to do my homework before I can go out.

3. She is doing her homework right now.

这些表达都清晰地传达了完成学校分配的家庭作业的意思。如果需要更具体地描述作业的类型，可以使用以下表达：

Do your writing assignments.

Work on your reading comprehension.

Do your math problems.

这些短语可以帮助你更准确地描述不同类型的学习任务。