Second language aquisition

Recently at a training session in Shillong , I was made to sit up and think once again. A teacher asked me if the aquisition process was different for adults and children. I gave her the usual answer maturity makes a difference blah blah.. but sumthin was making me uncomfortable from within.Catrherine Doughty has done extensive work instructed SLA versus self aquired SLA.But every research paper takes into account only a smaller section of society.Self instructed SLA by an adult is a fascinating field. How did we acquire proficiency in the SL?Usage in informal situation or through instructional learning?What constriants come in the place of SLA in an adult. I fo r one have noticed most adult learners of a target languagae cannot tune thier perceptions tophonetic segments.L2 always remains afected by l1 accent.the sensitivity to non native contrasts is yet another mechanism which gets left over in the processing .LAD being active till 12 yrs makes it easier for the child to ignore irrelevant details which makes them rapidly co articulate speech ,detect word boundaries and segmentation strategies.The late learner ,the adult in our case mismatches acoustic details.why then did the adults find it so much more difficult to wean out of the L1?ANy reader who wishes to add case studies i s welcome.