guptsingh123,
I'm also at school, and know exactly what your going through, lets deal with your issues one at a time.
school is maya at one of its peaks. Being surrounded by youth all intoxicated by kaam, one can really feel the effect it has on ones abhiyaas during school time. The best thing to do in these situations is to remain detached. Of course peers might say 'he's unsociable' but trust me, concentration will not decrease as you reduce the amount you listen to wasted breath spent on talking about kureiths and other such nonsense.
I also am unfortunate in that I cannot do amritvela with gursikhs, I reckon its a chance to develop our jeevan first then experience the laha of amritvela with sangat. Pyaar with Guroo sahib increases with abhiyaas. so the question is how do we do more abhiyaas?
Read more bani, maybe in your time after school you could engage in a sehaj part?
Not only does your maan move away from school issues, gurbaani will penetrate your maan inspiring you to do abhiyaas. Gurbani is the key to concentration, the more you read properly (trying to understand what Guroo sahib is trying to say) the more your concentration will increase.
Veerji, amritvela is a gift blessed by Guroo sahib. you should do ardaas and ask to be blessed with this gift. I know the disappointed of sleeping early and then not waking, but Guroo kirpa, your amritvela will get back to normal. Listen to kirtan as much as possible in school. Do abhiyaas in surtee and get on with school work instead of wasting time listening to rubbish.
Hope this helped. i'm a hardcore moorakh so forgive me if i've made gultia or offended you.
Take care jio, best of luck.
Waheguroojikakhalsawaheguroojikifatehh ji