Parent accessing child

I understand everything what is stated here, it describes how Child accesses Parent members. But, how about Parent Accessing Child? I just can't understand this. Why it is wrong? Could you please explain in terms of static binding rules during compile time? Here Student class itself becomes protected I guess, but why?

using namespace std;
class Person
{
public:
    int b;  
};

class Student : protected Person
{
public:
    int c;
};

int main()
{
    Student s;
    Person *pPerson;
    pPerson = &s;
    return 0;
}