Ask the teacher. While this may seem obvious, some people are reticent about asking a person's age. If you can find a way to casually slip the question into a conversation with the teacher, such as at a parent-teacher conference, you may get your answer easily.
Inquire of the school principal or superintendent. Ask if you can see the teacher's records or qualifications. While these may not state the teacher's birth date, the records will note where his degrees came from and when, which can give you a clue to his age.
Contact the Texas Board of Education (BOE). All Texas teachers must be registered and fingerprinted by the Board of Education before they begin teaching. You may be able to ascertain a teacher's birth date through her BOE information.
Use Spokeo. This website shows people's names, birth dates and a map of their homes. If the teacher has a common name, a Spokeo search may be difficult, but by limiting listings to Texas and looking in your city, you can usually find a person's birth date and address.
Look up the teacher on vitalrec.com, a website that lists birth, death and marriage dates. You can narrow the search to Texas, then pay to see the teacher's birth certificate.