If the student/parent does not reply to you within a week I recommend sending a second email to check in. Send this as a reply to the first email to keep the thread together.
Lesson opening
Hi [NAME],
I know how crazy email inboxes can be these days so I just wanted to follow-up about the lesson opening in case you missed it!
If you want to snap up this spot I recommend doing so quickly as lesson openings tend to fill up in a hurry! If this lesson opening doesn’t suit you, please let me know your availability so I can get in touch when we have a more suitable opening in the future.
Warm regards,
[YOUR NAME]