Yes. There's no requirement to agree with either classmate's post in TOEFL's Write for an Academic Discussion task — the scoring rubric rewards a clear, well-supported position, not agreement with what's already been said. Disagreeing with both posts is a completely valid approach, as long as you clearly state and support your own view.
Take the free TOEFL Benchmark Test and get your estimated band score in about 45 minutes.
Briefly acknowledge what the other students said before presenting your own view — this shows genuine engagement with the discussion rather than ignoring it, which is part of what's being evaluated. A pattern like "While [classmate]'s point about X is reasonable, I'd actually argue..." engages directly with the existing posts while still clearly staking out your own position.
Disagreement alone isn't enough — the same rubric applies regardless of whether you agree or disagree: a clear position, one well-developed specific reason, and ideally a brief acknowledgment of the strongest counterpoint. A response that just says "I disagree" without developing why scores no better than a vague agreement would.
Read worked Academic Discussion examples to see what separates a strong response.