Yep, I went to a fairly rural elementary school and the nurse, principal, and 5th grade teachers set up a couple intensive sex ed days where both 5th grade classes were grouped together and divided into groups of boys and girls.

Several rooms were set up into 'stations' about things like male/ female reproductive systems, birth control, STDs (or STIs), and things like that. Then the groups spent a couple days would go from station to station. Then at the end the nurse hosted a 'sex ed jeopardy' with all the 5th graders.

We had it a couple more times in 7th and 9th grade, but those were short curriculum segments in health/biology classes, unlike the 5th grade thing.