It sounds like 'ah-so' to me too. I think it's the student's family name 'Asoo' （麻生・朝生・阿相・阿蘇）or 'Aso' （阿蘇・安蘇・阿曽）. By the way, 'ああ、そう ah-so' or 'あっ、そう as-so' means 'Oh, I see.'. 'あ（っ）、そう' was Emperor Hirohito's favorite phrase/habit .

Ah-so It's kind of like 'Oh okay' or ' Oh, I see' in English. If someone were to say something you didn't know, you'd reply with ah-so. Ah is the sound that you make when you are listening to someone talking to signify that you're listening. So(u) is agreeing, sou is kind of like alright or okay. If someone was to say; Class is cancelled. You could say, ah sou. As to say oh is that so. ああそうですか？ Depending on how you say it you can make it into a question or agreeing to someone. ああそう - going up at the end and making the sou part longer is a question ああそう - taking a short break after ah, is agreeing or acknowledging the others point