Does attending a school like Ranger school count as non-rated time?

Any school whether professional or a specialty school will have non rated time; however, the 1059 that you receive from these schools should be annotated by your rater when conducting your annual evaluation. This will cover that "dead time".

I don't know if things have changed since I retired but your 1059 served as your rating document while you are in school.

I retired before the new rating system went into effect but this is what I found: From Army Regulation 623–3 Evaluation Reporting System and Department of the Army Pamphlet 623–3 Personnel Evaluation Reporting System

3–33. Preparation and submission requirements (2) Nonrated time encompasses periods of time when a rated Soldier cannot be evaluated. These periods include a Wide variety of circumstances when a Soldier is not performing duty in an assigned position under a valid rating chain. Qualifying periods of nonrated time are documented on OERs and NCOERs using nonrated codes and they become part of a Soldier’s rating history (see DA Pam 623–3). Comments on events or accomplishments during periods of nonrated time will not be made on OERs or NCOERs (see paras’s 3–16a and 3–17a).
(3) Gaps in a Soldier’s evaluation history may occur for various reasons. A majority of these gaps are acceptable, while others are unacceptable

Table 3–17
Reason codes for nonrated time for DA Form 2166–9 series NCOER
“S” Student at military or civilian school

School is considered acceptable. I couldn’t find where it specifically states whether or not a DA Form 1059 is submitted as an attachment to the NCOER but it does discuss it as part of the process. Normally the school Commandant is responsible for submission of 1059’s. For senior NCO promotion board consideration the board would already have your records. Not sure about semi-centralized junior NCO’s.

Noncommissioned Officer Evaluation Report Forms and Preparation
3–14. DA Form 1059 Service School Academic Evaluation Report