Borjas draws a parallel between the impact of immigrants on wages of the natives and the effect of FBTA on the US-born students.
US-born and FB students also have different views of communication skills and preparation of the FBTA vs.
The TA effect is tested with three binary variables: FBTA equals 1 if the TA is foreign-born, 0 if U.S.
One of the issues related to the FBTA variable, and perhaps to the COM2 and PREP2 variables, is whether its adverse effect is uniform across students with different abilities--that is, whether the marginal effect of FBTA is constant.
Applying the marginal effects concept to the student grade function, it could be argued that since academically poor students tend to be more dependent on the TA's tutorial, FBTA tend to have a stronger impact on them than on the better prepared students.
To examine the stability of the coefficient and the marginal effects for FBTA and some of the other key explanatory variables, a grade function is estimated for the full sample and a few sub-samples.
(6) The estimated grade probability function reported in Table 2 (second column) shows that GPA and FBTA are significant predictors of student grade.
To fully explore the impact of FBTA, in addition to the full sample, the grade function is estimated using six sub-samples as explained in Section II.
the foreign-born students to FBTA, estimates of the grade function are made for these sub-samples and results are reported in the last two columns of Table 2.
A significant finding here is that, in the math-track classes (column 2), FBTA does not seem to affect the probability of a grade significantly, perhaps due to the diminished importance of English language skills in mathematics classes.
The result for the FBTA confirms that FBTA adversely affect student grades in regular classes.
(11) The focus here is on the FBTA variable because it turned out to be the only statistically significant explanatory variable related to the FBTA and the perception of their class performance.