A The law is not completely clear about this but, broadly, leaves arrangements for a child within a school to the discretion of the head.
However, where a child has a statement, it is arguable that he or she should only be placed outside his or her chronological year group if the statement expressly provides for this.
The reason for this is that, otherwise, it may be argued that the child is receiving special educational provision (which is, in effect, provision which is different from that ordinarily available in local mainstream schools for children of that age).
In this case, you should consider carefully this child's statement to see whether such an arrangement is merited. However, ultimately, the law is likely to consider that it is your decision and a court is only likely to interfere in extreme circumstances.
David Ruebain is a partner specialising in education and disability discrimination at the law firm Levenes. www.levenes.co.uk