From the North:

I-405 South to the NE 124^th St exit
Turn east onto NE 124^th St
Stay on NE 124^th to Redmond Woodinville Rd
Turn right (south) onto the Redmond Woodinville Rd
Turn left onto 109^th St  -  109^th St becomes 104^th
Redmond High School is on your left 

From the South:

I-405 North to I-520 eastbound.
Go to the end of I-520 and I-520 becomes Avondale Rd
Follow Avondale Rd to NE 104^th St
Turn left onto NE 104^th St and continue up the hill
Redmond High School is on your right

From Seattle:

I-520 from Seattle to Redmond
Stay in left lane on I-520 as you approach Redmond
I-520 becomes Avondale Rd
Follow Avondale Rd to NE 104^th St
Turn left on NE 104^th St
Redmond High School is on your right at the top of the hill