As for SSOs versus ATC selection criteria mentioned by others. Again, two different disciplines. An ATC trainee's exposure to the role of SSO is so limited that the comments in this forum reflect badly on the posters.
Actually, I don't remember having to address any selection criteria for the ATC trainee job. I'll wait until I get feedback, but it may well have been a case of my not being very good at addressing the criteria, rather than not fitting the job. Especially since, as Duane said, the HR people are stretched to the limit.