He studies hard and always passes, but he gets himself so worked up he can't sleep. Both teachers and students benefit from tests. Teachers need to know what students have internalized from their lessons in order to select and focus subsequent lessons. Tests give them that information. Students need to review, organize, structure, recall and apply new learning to make it their own.
Tests measure their progress toward that goal.
There are several steps parents, teachers and students can take to diffuse test anxiety and improve student confidence and success as test-takers. Begin review well in advance of the test, so you don't run out of preparation time. Find out what the test will cover. Stay away from caffeine in coffee, soft drinks, chocolate, No-Doz and other sources. Caffeine interferes with sleep and can make you jittery.