How do I distinguish if 16-18 year olds are high school dropouts or still students using IPUMS CPS data?

I’m trying to calculate the share of each industry per state while controlling for individual educational level. In order to do that I regroup educational attainment into 4 categories:

(a) high-school dropouts,

(b) high-school graduates,

(c) some college (EDUC=080-092) and

(d) college+ (EDUC=100-125).

Note that the age group is restricted to include only working age population, i.e. 16-64 year olds.

For high-school graduates, taking into consideration what it is mentioned on another threat, I include only those who have completed 12th grade and received a high-school diploma or equivalent (EDUC=073).

However, the problem lies with high-school dropouts. In this category I include all individuals who reported 12th grade as their highest educational attainment but with no or unclear diploma (EDUC=071 & 072). I further include individuals who are older than 19 years old and who have completed 11th grade (EDUC=060) or lower grade.

My concern is how to handle the respondents between the ages of 16 and 18 with educational attainment equal to 12th or lower grade. How do I distinguish if they are still students or they are high-school dropouts? Is it correct to assume that all the individuals within this age group (16-18) who have been assigned an “NIU” in the IND1990 variable are still students and thus, exclude them from my analysis; while assuming that those who have a job (i.e. fell into one of the many industry categories available) are high-school dropouts?

Using IND1990=NIU to identify high school students will not be of much use, since a high school student working a part-time job would be in the IND1990 universe. For your purposes, the most helpful variable in IPUMS-CPS is SCHLCOLL, which identifies if a respondent was enrolled in high school during the previous week. Unfortunately, this measure understates the number of high school students during summer samples (i.e. May-August).

Hope this helps.