Pottstown school officials have denied a graduating high school senior the right to walk with her classmates at next Monday’s commencement because she will miss two of three practice sessions. Shawn Szydlowski will have to sit in the stands while other seniors pick up their diplomas because she is attending an orientation for a Muscular Dystrophy Association summer camp at the Variety Club Camp in Worcester.  She will also spend part of the summer at a Northern Pennsylvania Christian camp working with disabled people, something she says she wants to continue doing after she finishes college, where she plans to get a degree in special education.  The principal says the policy is clear.  Students must attend all three practices to walk with their classmates on graduation day.  He says there are exceptions, but this is not one of them.