已知数列\(\{a _{n} \}\)的前\(n\)项和为\(S _{n}\)，\(a _{1} =1\)，\((n-1)S _{n} =nS _{n-1} +(n-1)n(n∈N _{+} , n\geqslant 2)\)．
\((1)\)求证：数列\(\{ \dfrac {S_{n}}{n}\}\)为等差数列；
\((2)\)记数列\(\{ \dfrac {1}{a_{n}a_{n+1}}\}\)的前\(n\)项和为\(T _{n}\)，求\(T _{n}\)．