Are boys and girls allowed to be mixed during sexual education classes?

Sex ed is usually divided into different areas. One that can very well be mixed is when talking about STI's and reproduction. The other one is better if separated because that is when we talked about male and female puberty and how it affects their bodies and in order for the students to have the guts to ask things, we had it separated.

Added: It can depend on the prevailing laws and/or procedures of the local school district.