In primary school math class, letters and data are generally marked with pencils. The advantage of using a pencil is that you can easily correct mistakes, erase unnecessary parts and rewrite letters or data. In addition, the use of pencils is also convenient for students to think and adjust in the process of solving problems.

However, in some formal examinations and assessments, letters and data need to be marked with black pens. This is to ensure that the respondent's answer is clear and easy to read, and it is not easy to be modified or tampered with.

Generally speaking, it is a common practice to mark data with a pencil in primary school mathematics drawing problems. However, in some cases, you may need to use a black pen. What tools to use can be decided according to the requirements of teachers or exams.