Sen. Ron Young, a Frederick County Democrat, says animal dissections are no longer necessary. He also says alternative methods are cheaper, and 18 other states allow students to opt out.
But Sen. Nancy King, a Montgomery County Democrat, says local school boards can address the issue better than state lawmakers.
Republican Sen. Stephen Hershey, of the Upper Shore, noted that the measure required school officials to come up with alternative plans, just two months after the bill would have taken effect in July.
Only 13 senators voted for the bill. Thirty senators voted against it.