To Have and to Hold Back - S3-E13
Corrected entry: Lewis gets a scholarship to study science in the U.S. but was at risk of failing science earlier in the season. Even the fact that he was at risk of failing is a plot hole because he is obviously fascinated with science throughout the whole series.
Correction: Being fascinated with science or even getting a scholarship doesn't preclude a student from being at risk to fail. Many very bright and capable students struggle getting good grades when they don't complete assignments, have any behavior issues, don't do their class work, etc, especially if they find the pace of the class too slow.
Bishop73