We can tell how an amino acid will be classified (as polar or non-polar) by looking at it to see whether
1) it has a hydrocarbon chain or ring in its R-group; this will make it insoluble in water (and thus non-polar).
2) it has a charge (- or +) in its amino group; this will make it non-polar.
3) it has an electronegative atom (like oxygen) in its carboxyl group; this will classify it as polar.
4) it has a charge (- or +) in its R-group; this will make it polar.