Hello pragati, no you can't give the improvement exam if you have joined any course. The prerequisite of giving the improvement exam is that the concerned person must not be enrolled in any course while applying for or giving the exam . So, you can either join a course or you can drop a year to give the CBSE imrovement exam the following year , whichever you are comfortable with. Also if you lagged in just one subject , there is an option which allows you to give one exam the same year to improve your score . This exam is usually conducted by the CBSE along with those appearing for compartment papers . But again it depends on your choice to give the exam or not as the results are announced late around August when colleges seats are occupied.