In this section, “truant student” means a student: Who is unlawfully absent from school for more than: 8 days in any quarter; 15 days in any semester; or 20 days in a school year; and Whose absences for purposes of item (1) of this subsection are unlawful absences as defined by regulation. Each county board shall develop a system of active intervention for truant students. Each truant student attending kindergarten through 12th grade shall immediately be referred to the county board’s system of active intervention developed under this section. This section does not prohibit a county board from intervening in the case of a student who is frequently absent from school for both lawful and unlawful purposes, but is not a truant student.