The issue of "positive and negative acceleration" would be clarified for
students if a vector approach were adopted for kinematics, including
one-dimensional kinematics. The standard approach which introduces vector
quantities after one dimensional kinematics is an inconsistent one, as
displacement, velocity, and acceleration are no less vector quantities in
one-dimension than they are in two and three dimensions. By adopting this
approach, one discusses the components of velocity and acceleration
properly subscripting the quantities) in one-dimensional motion, which may
be positive or negative as they can be for all vector quantities. This
reduces the opportunity for confusion regarding the magnitude of a vector
quantity (always positive and with no subscript) and the components
(positive or negative and with subscripts). I have successfully used this
approach for many years both for translational motion and for rotational
motion about a fixed axis. I have submitted a note to The Physics Teacher
which includes more detail.