We consider eigenfunctions of a semiclassical Schrödinger operator on an interval, with a
single-well type potential and Dirichlet boundary conditions. We give upper and lower bounds
on the
-density
of the eigenfunctions that are uniform in both semiclassical and high energy limits. These
bounds are optimal and are applied in an essential way in
a companion paper to a
controllability problem. The proofs rely on Agmon estimates and a Gronwall-type
argument in the classically forbidden region, and on the description of semiclassical
measures for boundary value problems in the classically allowed region. Limited regularity
for the potential is assumed.