I agree with the other posts. I would also like to add that there are other ways besides technology. You can work one on one with the child, in addition to seating him or her front and center. Audio books are also very useful. Sometimes you can get these for free from libraries and centers for the blind. You can also record your own audiobooks and audio instructions with programs like audible.com.
It depends on what kind of auditory processing problems they are having. We have used the auditory trainer before and the students do not usually seem to like them. Teachers also have to be constantly reminded to use the microphone
The link below will give you some good information. I have used FM systems (auditory trainers) with some success. They help a child to filter out background noises. The teacher wears a microphone which feeds directly into earphones that the child wears. The earphones are small, and if it is presented to the child as being a cool item, like an Ipod, the child likes wearing the system. Be careful to turn off your mike when the child leaves the room, as we have had incidents of a child overhearing teachers' conversations from other parts of the school!
Assistive technology that you can use are augmentative and alternative communication systems. These systems can range from no tech, to low-tech, and lastly high-tech. These systems can also range in type from signs and gestures to communication boards and speech output systems.