Unfortunately, what they say is true and is borne out by the document that Lisa has linked. Your son has just turned 5 this term, therefore he does not have to be in full time education until next term. My own DD is an August baby and could theoretically miss the whole of her Reception year: legally, she does not have to attend school until Y1.
You need to concentrate on what they are doing to get him back into school in January.
My son has been excluded by head after less than two weeks in reception, for agressive behaviour, he has a statement and spd which they were not really taking seriously. And the dept are doing nothing to get him back to school, the head says its not the right school for him. she had complaints from other parents. As he has just turned 5 the dept seem to think he doesnt need to be in school til jan. which i dont agree with. Anyone got any advice or know if this is what the dept does with the first term.