According to dictionary.com concepts are 'an idea of something formed by mentally combining all its characteristics or particulars; a construct'. In other words  a concept uses knowledge (known as semantics, see section on semantics for more information) about an object or idea and is able to tell the difference between two totally different ends of the  same spectrum. This is easier to understand with an example such as  big and small. Big and small is an easy concept as it is very visual, however, as we get older we realise that it is also relative and even this easy concept may be hard to understand for children as they are learning. The easiest way to learn concepts such as these is to give extreme examples such as a very big Teddy and a very small  Teddy.  

Concepts that are not visual such as time and space can be even harder for the child to understand and once the child is in primary school these can be the ones that are most difficult or cause most difficulty in classroom. When working at developing concepts it is important to first find out what concepts the child understands and what they don't. The concepts the child  understands can be used to reinforce how a concept  is learnt and help to learn new concepts. It also helps as you can focus on the concepts that are needed most. If the child is having difficulty with most concepts this is more difficult but starting with the concepts that the child is likely to be able to see or is interested in is a good starting point. For example if a child is interested in planes using a big plane and a small plane to teach big and small can be very useful as they are more likely to concentrate on the task in hand.