Short answer. Yes. Article 97, as rewritten by Republic Act No. 10592 (2013), gives every qualified prisoner an extra fifteen-day deduction from his sentence for each month he spends in study, teaching, or mentoring service — on top of the ordinary good-conduct time allowance already earned for that month.
What the law says
At any time during the period of imprisonment, he shall be allowed another deduction of fifteen days, in addition to numbers one to four hereof, for each month of study, teaching or mentoring service time rendered.
Revised Penal Code, Article 97 — Allowance For Good Conduct. Read the full provision →
The study, teaching, or mentoring allowance
Article 97 sets out a scale of ordinary good-conduct deductions, and then adds a separate one on top of it: at any time during the period of imprisonment, he shall be allowed another deduction of fifteen days, in addition to numbers one to four hereof, for each month of study, teaching or mentoring service time rendered. This allowance is cumulative with the ordinary good-conduct credit for the same month, not a substitute for it, and it is not tied to how long the prisoner has already served.
The ordinary good-conduct scale it builds on
The base allowance in Article 97 rises the longer a sentence runs: twenty days off for each month of good behavior during the first two years, twenty-three days a month from the third through the fifth year, twenty-five days a month up to the tenth year, and thirty days a month for the eleventh year onward. The fifteen-day study, teaching, or mentoring credit is added to whichever of those figures already applies to the prisoner's year of confinement.
A 2013 update, and appeal does not forfeit it
This scale is the text of Article 97 as amended by Republic Act No. 10592 (2013), which raised the deduction days and added the study, teaching, and mentoring credit that did not exist before; older reproductions of the Code still show the smaller pre-2013 figures. The article also protects the allowance from one common worry: an appeal by the accused shall not deprive him of entitlement to the above allowances for good conduct, so filing an appeal does not cost a prisoner the credit already earned.
Who this allowance is available to
Article 97 opens the good-conduct scale to any offender qualified for credit for preventive imprisonment as well as to any convicted prisoner in a penal institution, rehabilitation or detention center, or local jail. The study, teaching, or mentoring credit rides on that same eligibility — it is not limited to sentenced prisoners only, but reaches qualified detainees still awaiting the outcome of their case as well, provided the underlying good-conduct requirement is met.