I think everybody will admit that the guy was wrong. I don't think that's an issue. You can't be a teacher and be dating a student.
However, should it really be a felony? I mean, if it's forced or the victim is unreasonably young, then OK, but as a former teacher I can tell you that there are LOTS of these types of things that go on, and as we've seen, it's not just males. Most last a few months and then go away. Even if the school knows, most do not pursue these cases if, like in this case, it's a relatively young teacher and a relatively old student (16+) due to the legal costs involved. It's easier for the district to basically tell the teacher that they know what was going on and the teacher needs to go away. The teacher gets the crap scared out of them, they move on, and hopefully they learn their lesson. This is not always the case.
Also, there are LOTS of married husbands and wives that first knew (not in a dating way) each other as teacher/student. I personally know of several couples. Now they didn't start seeing each other until afterwards, so that makes it OK. In fact, 2 didn't start seeing each other until WAY (2-3 years) after. The other basically acknowledged there was an attraction there (there was 3 years difference in age) while they were student/teacher, but made the conscious choice to basically stay away from each other (they didn't talk about it, but she said she could tell what he was doing when he changed the way he started acting toward her aka he wasn't as friendly, didn't joke around, etc.). Graduation night came, he was there and left her a little note on her car. She called him up and they dated for 3 years before getting married.
At any rate, I don't think it's professional to have a relationship with a student that is 16+. It's not good for the student or the class. However, I think it's borderline immoral, just like I think it's probably borderline immoral for a 25 year old to date an 18 year old. It depends on what they're after. People have different maturity levels. Girls are typically older than guys at that stage of life, so it's natural that they are looking for someone older (aka more mature). Add in a guy who's maturity level is a little under what the average guy is, and there you go. Also, some of these people are in it for a f*** and some are actually interested in pursuing a relationship. Does it make college guys that are trolling for an easy HS f*** a crime? No. It just depends on intentions, and that's where it starts getting gray.
So personally, I think that a relationship with a 16+ year old student should result in the loss of the teaching license and misdemeanor. Losing your job and being unable to work in most of the profession ever again is no slap on the wrist. I think DWI is a MUCH more serious infraction than this, but people do that every day and end up with a suspended license and a heavy fine.
Now if it becomes a habitual thing, that's another story. You get busted more than once and then I think you have to start looking at some LIGHT jail time, increasing in severity from there on.
However, for ANY legal remedy to apply, you have to have school districts that are willing to bring charges (aka put someone on leave while an investigation occurs). Right now, schools are too scared of doing that to someone and the investigation turning up squat. At that point, the teacher and the teacher's union will basically bend the ISD over.
