I'm not about to start a moral debate on homosexuality and lesbianism. I have my own opinions about this subject, but let's keep it that way.
To be honest, I think all schools in Singapore will not tolerate homosexuality or lesbianism, exhibited publicly or otherwise, in their school premises. Especially so when the parties involved are wearing the school's uniform. Conservative parents will most likely not want to enrol their children in that school.
What consenting adults do behind closed doors is entirely their choice and preogative.