No. The work which this teacher did in the school, as part of his normal teaching duties, while he was employed by you, belongs to the school and not to him.
If he were to use the same material to write a boo or produce a teaching pack for publication, that would, of course, be his, but his attempt to extract money from you for work which he was paid to do in the first place can only be described as barefaced cheek.
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