We know that younger students have shorter attention spans.
Kindergarteners 5-6-year-olds are able to focus on a task for 10 - 30 minutes
First-grade students can focus for 12 to 35 minutes
Second-grade students can focus on a task 14-40 minutes
The time really varies a lot for each student. Many schools recommend activities lasting the age of the students +1 minute as a rule of thumb. You will want to work with parents to establish what works best for each student.