Performance in school varies, it can go up and down, or be always high or low. Sometimes performance plummets down. Reasons for this are similar to attendance problems, see this area for more info.

There are some problems that may affect performance, such as:-

General or specific learning problems, like dyslexia, dyspraxia. Most of these are picked up by teachers in primary school, but sometimes its important to get these checked out.

Memory problems, again, usually picked up in primary school

Attention and concentration problems, lots of reasons for this, including:-

a) Depression

b) Tiredness

c) Hearing difficulties

d) Anxiety, worries about things outside of school

e) Dis-interest in subjects or work in general

f) ADHD, attention deficit hyperactivity disorder, usually picked up in primary school

The best way of sorting these problems out is to talk to a teacher, parent or school adviser, especially if stressed, or depressed or very anxious.

But, if you want to sort it out yourself, try the Log-in and self assessment. There are also some links to various tests, but don't take them too seriously, you need to get proper assessments done, if you think you have some learning problem

BBC, education
Shrinktank, various intelligence and other tests