POCO helper class refactoring
Implement this interface in all of your Dto where it needed:

interface ICommonDtoStuff&lt;T&gt;
{
    bool IsSelected { get; }
    T ID { get; }
}


Then you can create a method like this:

public IList&lt;T&gt; GetSelectedResults&lt;T, U&gt;(IEnumerable&lt;U&gt; scores) where U : ICommonDtoStuff&lt;T&gt;
{
    return scores.Where(x =&gt; x.IsSelected).Select(x =&gt; x.ID).ToList();
}


As extension method:

public static class Extensions
{
    public static IList&lt;T&gt; GetSelectedResults&lt;T&gt;(this IEnumerable&lt;ICommonDtoStuff&lt;T&gt;&gt; scores)
    {
        return scores.Where(x =&gt; x.IsSelected).Select(x =&gt; x.ID).ToList();
    }
}