Is it permissible for the teacher to take payment in advance as a guarantee of his right, and is he entitled to take money for a session that the student intentionally missed?

There is no objection to you stipulating the prepayment of the fee from those you teach. If you contract with students to teach them and exert yourself for that, then you have the right to take the fee from them even if they do not attend. This is because a private contractor is entitled to the fee by making himself available to the employer during the hire period, whether he works or not. When a contract is made absolute, the fee becomes due by virtue of the contract itself, and its delivery is due upon the expiration of the period or the completion of the work. The fee becomes fixed upon the utilization of the benefit or the passing of the period.