for SLS admission, WP will take any test score you have. for most applicants, it will be the PSAT, but feel free to submit ACT and/ or SAT scores if you have them.
We were told that attending SLS does not so to speak increase ones chance of Admission or an LOA. we were told however that by being selected to attend SLS, we were already deemed qualified applicants, but still we must complete the application process just like everyone else. SLS will not give you a special advantage and it does not guarantee anything.
Source: I attended 2012 SLS Session One and this is roughly what all the admissions representatives were telling us.