Being home for sem is very different than being away. One, you can learn with a blank mind, able to absorb a lot more since you dont have the same pressures as being at home (learn instead of babysitting your sisters), learn from brilliant teachers (that you didnt have in high school).
Two, making friends that can last a lifetime, is important. they can help you with life’s struggles for years afterwards. Many people have real struggles and these friends can help one through it. I know someone who if not for her sem friends who care deeply about her and all I dont know how she would be able to manage. The girl told me that her high school friends are not in touch the same way.
Three, the reason BYs were created was because sarah schneirer found that mothers were not able to teach their daughters like in the olden days. Maybe in the sephardic ones they are able to, but it seems like in the askenazic world girls really do need to go learn in schools. Yes, they can learn to cook and clean from their mothers but is that all motherhood is about?
Four- sem has to be treated as something different that 12th grade. It isnt 13th grade. It is a year to package up all you learned, like take a mashal of a computer. You built a computer for 12 years, drilling the oil for plastics, creating the computer chips ect. Then you want to give it so you make all the final upgrades, add some extra software and RAM, and boost the speed a little. Then you package it with wrapping paper and a bow. Sem is that last stages. At the beginning they work hard to add the extra RAM and software. Then, the last couple of months (purim to the end) is about the packaging. What to take with you for life. How to apply all you learned in the past. It is very different and can change a person for life.