This is all tripe. First of all the Swiss love this psychologist bullshit, in the real world a doctor will refer you to a psychologist, in Switzerland a schoolteacher. Considering that majors first school teacher didn't know the difference between a jaguar and a leopard you can imagine my thoughts on her qualifications to call in a psychologist.
Its also crap about having to know geography - thats something for secondary school.
If I were you i would go on the offensive - All info here with ref to Kt. ZH
1.) The test your son was given does not reflect the material taught in class
2.) The test was not an certified aptitude test and the language element not available in English, therefore unsuited to the issue at hand.
3.) You make schooling decisions in class 6, not class 5, you son has a whole year to find his feet.
4.) Promise them you wil send him to German classes over the holidays - that will take the language wind out of their sales.
5.) Avoid a Realschule at all costs. Sek is, in Kt. ZH, divided up into A,B,C. and focuses towards getting an apprenticeship. Sek C is to be avoided at all costs. Sek A is the minimum you should be aiming for and necessary in order to get a decent apprentiship or, what you really should be aiming for, to get into Grammar school after 2-3 years of Sek.
6.) The quality of Sek A depends on where you live - on the Gold Cost the standard is good, in Schwammedingen (sp.) pretty ****. I suppose a British comprehensive would be roughly equivalent.
Edit: I see Argau has 5 primary classes but the timetables are downloadable - check what the kids do in their first Sek and is it what the psycho says it is - In my opinion you would be better off getting the kid into Sek and, if absolutly necessary to repeat 1st Sek.