Hello sir,
Yes there is a chance that your son can change to science in class 11th after completing his high school form commerce stream, but it totally depends on the school that they would give admission to a commerce student into science stream as the science stream have always been classified tougher than that of commerce stream.
But the commerce stream is also a very good stream to pursue as it provide very good jobs with a high salary structure.
Here is the brief comparison of both the streams:
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