Hi my ds (5) has a form of epilepsy - no name but he was dx'd when he was 3. He has had absense siezures, myoclonic jerks and one tonic clonic fit which landed him in hospital.
I say "had" as he is well medicated at the moment and we have seen no fits for over 12 months 
He was a terrible sleeper pre medication and a sleep induced eeg showed multiple fits while he was sleeping, none of which were apparent in RL so were sort of sub-fits iyswim.
Re development - he has a SLI and is currently about 2 years behind with his speech but is making fantastic progress (had no speech and used only Makaton 18 mths ago). He is now able to form sentences correctly and rarely uses signing.
He is Yr1 now and is holding his own in school although he is still behind (approx 12 mths). Best thing is hes happy and learning.
I have raised the question as to whether the epilepsy has caused the learning delay or whether the learning delay and the epilepsy are a symptom of a problem elsewhere with his pead only to be told that we may never know!
One thing I was told that should an absence occur when the brain is trying to "log" a new experience or consolidate new information, then a "gap" will appear in that info pathway which might mean that the thing hasn't been learnt properly. Its almost like falling asleep in class and missing half the lesson! Even small "zone outs" can have an effect.
The good news with us is that if DS stays fit free for another 8 mths and has clear eegs then we will be starting to wean him off his meds 