most children will:

describe the main functions of their skeleton; describe observable characteristics of bones; recognise that their skeletons grow as they grow; state that movement depends on both skeleton and muscles; identify a question to be investigated and how to collect and interpret reliable evidence in order to answer the question

some children will not have made so much progress and will:

state that they have skeletons; describe some observable characteristics of bones and make measurements when investigating a question

some children will have progressed further and will also:

state that when one muscle contracts another relaxes and make an evaluation of the extent to which the evidence collected to answer a question supports the prediction made