The incoming seventh grade class has a choice of French or Spanish as English electives. There are three times as many Spanish classes as friends or 3 to 1 how many students can choose Spanish if there are 850 students round to the nearest whole number.
Since there are three times as many Spanish classes as French classes, we can assume there are 3x French classes as well.
Let x represent the number of French classes.
Therefore, the number of Spanish classes is 3x.
The total number of English elective classes is x + 3x = 4x.
Since there are 850 students, each class contains an average of 850/4x = 212.5 students.
The number of students who can choose Spanish is 3x * 212.5 = 637.5x.
Since the number of students must be a whole number, we can round down to the nearest whole number.
Therefore, the number of students who can choose Spanish is 637 students. Answer: \boxed{637}.