How To Surprise A Middle School Son

I am not a hovering parent. I am not interested in PTA, class parties or chaperoning anything. I would be happy if they had school all year. For the last parent teacher conferences I wrote the teacher a note and said "I do not feel the need to come in for a conference.  My son likes school, his teachers, his peers and his subjects.  Of course I will come in if you feel any need at all, but I do not have any problems or concerns I would like to discuss. Would this be ok with you if we do not have a conference?"  And my kids are ok with this too. We try to raise them to be self motivated, and study hard and work hard and play hard to please God and themselves. To have the desire in their hearts to study and learn and want to get  A's.  So far it seems to be working. I don't have to ask if they did their homework or studied for a test...they take care of their studies themselves..and ask for help, a lot, if they need it.
So , I got a letter from the principle of the middle school informing us our son was going to be recognized in front of the school at the end of the year and we should come in for the ceremony. But it is a surprise and we should please not tell our son he is getting this award.  I go into the auditorium and wait.  Interesting to watch the interaction of all the students, filing orderly into their seats. I am sitting on the end and I see my kid, with all his friends that I know so very well because they are at my house all the time. My son is standing 2 kids away from me and I can hear him saying to his friends, "Look there are parents here. My mom doesn't even know where this school is."  and his friends see me sitting there and just start cracking up.  My son thinks they are laughing at a joke he may have made or something and elaborates even more, "I am serious. She doesn't even know this school HAS an auditorium.  She would never come to whatever it is going on now."  They are holding their stomachs laughing and my son is standing right by me talking about me and he has no idea I am there. This is very funny to 6th grade boys, but my son does not think what he is saying is THAT funny. So he says, "Like what?  What is so funny?"  And then he looks at me. Silence. He is expressionless. And frozen still. Like I am a ghost. The line moves but he doesn't. He finally says, " Wait. What are you doing here?"and he has to go because he is holding up the line.