Schools may not be compelled to keep those precise figures - I don't know - but I see no reason why you can't get hold of the information by putting in a FOI request.
There are legitimate grounds for refusing a FOI request, e.g. if individual children might be identified, or if the work involved in gathering the information would be excessive. (I can't see why the latter would apply, though - a SENCO could probably come up with the figures in less than a minute!)
FOI requests should be made in writing to the relevant admission authority (i.e. the school or the LA as appropriate). You can do this directly, or another possibility is to use the following website: http://www.WhatdoTheyKnow.com
(However, it may be necessary to ask them to add the admission authority to their list of public bodies first.)
If you encounter any problems with the admission authority, it would be worth contacting the Information Commissioner's helpline (on 0303 123 1113 or 01625 545745, which is available between 9am and 5pm, Monday to Friday) for advice.https://www.ico.gov.uk/Global/contact_us.aspx