This indeed a very big problem for him as it will cause him many problems in his academic life. There are many techniques for increasing one's writing speeds. Below are given some methods:
1# One of the most effective ways to enhance writing speed is to practice writing within a particular time. The goal to be able to write faster cannot be achieved just by trying once - it will be acquired after a set of attempts.
2# To write faster, you just have to have the willpower. Only trying won't help - you should also have the desire to become a fast hand-writer.
3# He must be pushed by his teachers, parents and friends to write faster, in the case, he is not paying attention to his problems and not trying. This should make one tend to write faster.
Advices such as these should be suggested to the particular student. If he is co-operated by everyone, then, no one can ever stop him to topple his faults - a slow handwriting.