Learn Hardcore Russian: Во время практики в школе я буду объяснять грамматику детям. - During the practicum at school, I will explain grammar to the children.

The basic preposition is в, but Russian sometimes uses во instead for easier pronunciation. Here, в время would be awkward to say, so it becomes во время.

Also, во время is a fixed expression, and it requires the genitive case after it:

во время урока = during the lesson
во время каникул = during the holidays
во время практики = during the internship / practical training

Why is it практики and not практика?

Because во время requires the genitive case.

The dictionary form is практика, but after во время it changes:

практика → nominative
практики → genitive singular

So:

Во время практики = during the internship / during the teaching practice

What does практика mean here?