When time comes for you to make a speaking class for your students the best way of challenging the topic and your students is to be be against the positive effects of topic and seeing the faults of issue of course with firm reasons to support your idea

for example in yesterday's speaking,the topic was
the effects of science and technology in our life,bcs everyone agreed on the benefits of science and technology,I was against them bcs I believe the abuse of technology is killing people as what nuclear weapons are doing,or as you see the country which has more technology kills more,for example the U.S has the technology of killing people in very advanced form.