Ed V's answer above--which I am accepting--has enabled me to answer my own question. I am just posting this because my confusion was not too hard to resolve once I saw the quantities involved and someone else may have the same confusion.

The short of it is: student polarimeters measure circular birefringence (CB), usually at a specific frequency, concentration, and sample length. Optical rotation is an aspect of CB.

The Wikipedia article on optical rotation conveys the following: in student polarimetry we speak of "plane polarized light" but this is best thought of as a superposition of left- and right-circularly polarized light. In an optically active solution the difference in transmission of the L and R components is ascribed to a difference in refractive indices $\Delta n$ which causes the measured rotation,

$$\Delta \theta = \frac{length\cdot \pi~ (n_L-n_R)}{\lambda}. $$

An optically active material may be described as circularly birefringent if it discriminates between L and R components of circularly polarized light according to the above relation, and so the rotation of plane polarized light through an angle $\theta$ is an example of circular birefringence. Here is a definition-oriented link.

The optical rotary power is closely connected to $\theta$ and varies (as does $\theta$) with the frequency of the light. The variance of $\theta$ with frequency is called optical rotary dispersion (ORD). Its cousin, circular dichroism (CD), is due to differential absorbance ($\Delta A$) of L and R light and also varies with wavelength. The remarkable connection of ORD and CD via the Kramers-Kronig relations (not so easy to demonstrate in practice, I guess) is described in ron's answer (linked above).

Ed V's answer above--which I am accepting--is correct and also allowed me to reach the conclusion on my own. I am just posting this because my confusion was not too hard to resolve once I saw the quantities involved and someone else may have the same confusion.

The short of it is: student polarimeters measure circular birefringence (CB), usually at a specific frequency, concentration, and sample length. Optical rotation is an aspect of CB.

The Wikipedia article on optical rotation conveys the following: in student polarimetry we speak of "plane polarized light" but this is best thought of as a superposition of left- and right-circularly polarized light. In an optically active solution the difference in transmission of the L and R components is ascribed to a difference in refractive indices $\Delta n$ which causes the measured rotation,

$$\Delta \theta = \frac{length\cdot \pi~ (n_L-n_R)}{\lambda}. $$

An optically active material may be described as circularly birefringent if it discriminates between L and R components of circularly polarized light according to the above relation, and so the rotation of plane polarized light through an angle $\theta$ is an example of circular birefringence. Here is a definition-oriented link.

The optical rotary power is closely connected to $\theta$ and varies (as does $\theta$) with the frequency of the light. The variance of $\theta$ with frequency is called optical rotary dispersion (ORD). Its cousin, circular dichroism (CD), is due to differential absorbance ($\Delta A$) of L and R light and also varies with wavelength. The remarkable connection of ORD and CD via the Kramers-Kronig relations (not so easy to demonstrate in practice, I guess) is described in ron's answer (linked above).