Will smoking effect me academicaly

Assuming you're not skipping out on classes to smoke, anyway, nicotine actually causes a very slight increase in mental alertness in most people. A small number of people may find that smoking improves academic performance (calming them before tests or while studing), but most will see no effect whatsoever in their grades (the effect is very small).

The effect is definately not large enough to justify the health risks of smoking, but smoking does not ipso facto make one stupider (or smarter) - although it may certainly make other people think you're stupider (almost never smarter). That's perception, though, and not quantifiable.

For comparison, listening to 20-30 minutes of classical music per day has a significantly larger effect on intelligence.