After the teacher isolated Kumar from the rest of the class, he calmed down and explained his outburst to the student.
After the teacher isolated Kumar to the rest of the class, he calmed down and explained his outburst to the student.
After the teacher isolated Kumar from the rest of the class, he calmed down and explained his outburst to the student.
After the teacher isolated Kumar to the rest of the class, he calmed down and explained his outburst to the student.
The verb "isolate" always idiomatically takes the preposition "from."