Final answer:
The correct placement of the comma in the sentence is around the word 'however'. It should read "He was, however, very successful in his math classes," with commas providing the necessary separation for the transitional word.
Step-by-step explanation:
The comma in the sentence "He was however very successful in his math classes" belongs around the word however. This is because however is an introductory element to the rest of the sentence, providing a contrast or a pause to the statement being made.
The correct punctuation would be "He was, however, very successful in his math classes." The use of commas around however indicates that the information could be omitted without changing the basic meaning of the sentence, making it nonessential.
In general, when using transitional words or phrases like however, they should be enclosed by commas to separate them from the rest of the sentence.