You can use this to solve your problem:
private async void btn_Go_Click(object sender, RoutedEventArgs e)
{
HttpClient webClient = new HttpClient();
Uri uri = new Uri("http://www.school-link.net/webservice/get_student/?id=" + txtVCode.Text);
HttpResponseMessage response = await webClient.GetAsync(uri);
var jsonString = await response.Content.ReadAsStringAsync();
var _Data = JsonConvert.DeserializeObject <List<Student>>(jsonString);
foreach (Student Student in _Data)
{
tb1.Text = Student.student_name;
}
}