Matus filed a contempt action against her former husband, Mattocks, for his failure to pay certain college expenses for one of their sons. She alleged Mattocks was obligated to do so by the agreement incorporated into the parties’ 1980 final judgment and decree of divorce.1 The agreement provided that the specified educational expenses be “paid by the Husband for such purpose only so long as each child is enrolled in college as a full-time student, seeking a four year college degree.” (Emphasis supplied.) The superior court found that the son, who was then 23, at all times had been enrolled as a full-time student in a four-year degree program. It ordered Mattocks to reimburse Matus for past expenses and to pay for future ones so long as the son was enrolled in a four-year degree program on a full-time basis “as defined by the University of Georgia.” We granted Mattocks’ application for discretionary appeal, and we reverse.
Mattocks’ obligation to provide for the educational expenses for his adult son arose solely from the agreement between the parties. See Marshall v. Marshall, 262 Ga. 443 (421 SE2d 71) (1992); Coleman v. Coleman, 240 Ga. 417, 422 (5) (240 SE2d 870) (1977). The plain language stated that the obligation was “only so long as” two conditions existed. The son had to be enrolled full time and in pursuit of a four-year college degree. The trial court found both conditions satisfied; however, it did so after assessing the son’s attendance by evidence of course load and credit hours. This was error. There was no evidence that the parties intended this standard as the agreement. Moreover, this Court has otherwise construed “the phrase ‘full time student’ to mean continuous attendance during the normal school year.” Hayward v. Lawrence, 252 Ga. 337, 338 (312 SE2d 609) (1984).
The evidence was undisputed that the son was not in continuous attendance for the duration of the normal school year after the conclusion of the 1989-1990 academic year. During that first year, the son was enrolled in a private college and on partial scholarship. He chose to leave school after he learned that his scholarship grants would not be renewed for academic reasons. He worked, joined the military, and did not resume his college education until approximately 15 months later when he entered the state university system.2
Thus, Mattocks’ support obligation for the son’s educational ex*347penses ended at the conclusion of the 1989-1990 academic year when the son ceased to be a full-time student within the meaning of the agreement. The agreement did not call for a resumption of payment by the father following interruption of his son’s college attendance, and the trial court in this proceeding was without authority to modify the agreement to provide otherwise. See Still v. Still, 199 Ga. App. 723 (405 SE2d 762) (1991).
Judgment reversed.
All the Justices concur, except Sears and Hunstein, JJ., who dissent.Matus sought reimbursement for educational expenses for the 1991-1992, 1992-1993, and 1993-1994, academic years and an order requiring Mattocks to pay for such expenses during the next two years in which the son was enrolled in the state university system.
The son’s attendance at the state university was interrupted in the spring of 1993 and again in the winter of 1994.