The short answer is "maybe." Education curriculums are set locally or at the state level; so if you want to know exactly what your child's school is teaching, you'll have to talk directly to the school or district officials. According to a 2005 Gallup Poll, a little over half (58 percent) of teens aged 13 to 15 had received sex education at school. So some middle schools are definitely providing some sex education, but the follow-on question is what type of sex education is being provided.
Sex education programs generally fall into one of three categories: abstinence-only, safe sex approach, or a combination of the two. According to the same Gallup Poll, almost two-thirds of schools are offering the safe-sex approach curricula, while less than a third are offering the abstinence-only approach (the rest either didn't know or didn't answer the question) [Source: Gallup]. The United States government has provided federal funds for abstinence-only programs since 1996; however, that funding was discontinued in 2010. A study of middle-schoolers who were given sex education in school showed that the abstinence-only option was more effective in delaying teen sex than the safe-sex approach [Source: Gay].
So it's clear that some middle schools are providing sex education. However, another study questions whether starting sex education at middle school is already too late for some youngsters. Researchers at the University of Texas School of Public Health looked into the sexual activity of middle-schoolers in 2009. They found that while most middle-schoolers had not yet engaged in any type of sexual intercourse, an appreciable percentage had. Specifically, of the study's participants 12 years old or younger, twelve percent had engaged in intercourse, almost eight percent had had oral sex, six and half percent had anal sex, and four percent had engaged in all three types of sex [Source: ScienceNews]. The researchers concluded that the comprehensive prevention programs needed to be implemented at the proper age.