The student called quiet may be doing the lesson in two languages internally.

The quiet student may be translating. Every question arrives in one language, gets worked in another, and the answer has to be built back before it can be said, which takes time that looks like hesitancy. Doing the whole lesson twice is significant work and it presents as not participating.

Allow more time before reading silence, and offer written responses where you can. If this describes you or your child, saying so plainly to a teacher usually helps. What looks like reluctance is often a longer route being travelled at full speed.