The first is derived from शिक्ष् अ विद्योपादाने भ्वादि 389
शिक्षते -
and the derived forms from the root can be found in the above link in the Dhatupatha. The second is derived from the root
शासु शास् उ अनुशिष्टौ 2 अदादि 82
with अ suffix in the feminine gender - meaning learning.
and the derivatives could be found in the following pages:
including conjugations and variations.
शास् + य - "शास इदङ्हलोः" - शिष्+य > शिष्यः; एतिस्तु - ( ३।१।१०९) - क्यप्;
शास् + क्त - " ” .................>शिष्+त > शिष्टः।